For the pivotal train crash during Reel 2, Burtt faced a major challenge – how to sustain the tension without overwhelming the soundtrack. “My thought process was: How do you build to a climax when the first sound in the sequence is justifiably equally as loud as the last?” he offers. “I wanted to leave spaces in the sound effects so that the audience could appreciate discrete events without it becoming too muddy [as sounds build on one another]. I had a range of metal crashes and explosions that I time-stretched, pitch-shifted and processed to create choreographed sequences that continually build [as the full extent of the crash is appreciated]. My final decision was that there should be no overlapping sounds; each element would have a specific start and finish.”